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Lowering nitrous oxide emissions? There’s a map for that

CIMMYT scientists map global hotspots for nitrous oxide emissions from maize and wheat production, setting a clear path for emissions reduction efforts

A farmer in Ethiopia prepares to spread urea fertilizer by hand in his field after the sowing of wheat.

Like many issues besetting agrifood systems today, the question of nitrogen use appears to yield contradictory problems and solutions depending on how and where you look. Many parts of the globe are experiencing environmental consequences due to excessive nitrogen application while, in other parts, agricultural productivity is severely affected by low nitrogen.

Maize and wheat systems are at the heart of this dilemma, as they account for around 35% of global nitrogen fertilizer usage and play a critical role in ensuring the food security of a growing population.

Addressing this issue means ensuring that nitrogen is applied with maximum efficiency across the world’s croplands. Farmers should be applying only as much nitrogen as can be taken up by their crops. Apply more, and the excess nitrogen is lost to the environment in different forms, including nitrous oxide (N2O) emissions — a potent greenhouse gas. Apply less, and agricultural potential goes unmet.

Given the twin challenges of global climate change and the projected need to increase global food production over 70% by 2050, neither scenario is desirable.

Tackling the problem first requires an accurate accounting of N2O emissions from global maize and wheat fields, followed by quantification of the potential for farmers to mitigate nitrogen emissions, disaggregated by region. In 2021, scientists at CIMMYT, in conjunction with researchers at the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS), accomplished this important step in a study published in Science of the Total Environment.

“Spatially explicit quantification of N2O emission and mitigation potential helps identify emission hotspots and priority areas for mitigation action, through better nitrogen management, consistent with location-specific production and environmental goals,” said Tek Sapkota, CIMMYT’s climate change science group lead and review editor of the Intergovernmental Panel on Climate Change (IPCC)’s sixth assessment report.

Quantifying greenhouse gas

CIMMYT scientists and partners quantified N2O emissions using four statistical models, which were validated against actual measurements recorded at 777 globally distributed points.

They found that, for both maize and wheat, emissions were highest in East and South Asia, as well as parts of Europe and North America. For maize, parts of South America also appeared to be emissions hotspots. In Asia, China, India, Indonesia and the Philippines were major emitters for both crops. Researchers also observed that China, along with Egypt, Pakistan and northern India have the highest excess nitrogen application.

A girl prepares wheat seeds for sowing in Ethiopia

Trimming the excess

Specifically identifying hotspots of excess nitrogen application is important, as they represent promising areas to target for emissions reductions. For a given region, the volume of emissions may be a factor of large maize or wheat cultivation areas, coupled with high levels of nitrogen usage. Farmers may not have much room to reduce nitrogen application without affecting their yield — and reducing the area under cultivation may not be desirable or viable. Where the rate of excess nitrogen application is high, however, reducing the rate of application and increasing the efficiency of nitrogen use is a win-win.

The researchers estimate that a nitrous oxide emission reduction potential of 25-75% can be achieved through various management practices, such as the 4Rs, which stand for the right source, right timing, right placement, and right application rate. The case for emissions reduction potential of 4R management practices was bolstered by a meta-analysis also published in 2021 by a team of scientists that included CIMMYT researchers.

Not only would such a reduction drastically reduce N2O emissions and lessen other environmental impacts of maize and wheat production, but it would also represent significant cost savings to farmers. Improved efficiency in nitrogen application can also have positive effects on crop yield.

“Promoting integrated nitrogen management approaches through the right policies, institutional support and good extension systems is essential to improving the use efficiency of nitrogen in order to meet food security, climate action and other sustainable development goals,” Sapkota said.

Kindie Tesfaye, a CIMMYT scientist and lead author of the mapping study, commented on its policy importance. “The estimated mitigation potentials from global maize and wheat fields are useful for hotspot countries to target fertilizer and crop management as one of the mitigation options in their Nationally Determined Contributions (NDCs) to the United Nations Framework Convention on Climate Change (UNFCCC).”

A farmer sows wheat by hand in Ethiopia

This work would not have been possible without the support of our partner, the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS), which provided the needed funding.